The investigational drug Flavone acetic acid (FAA) upregulates the genes for IFNs -gamma and alpha as well as TNF-alpha, and synergizes with rIL-2 for the treatment of murine renal cancer (Renca) and the C26 murine colon carcinoma. Subsequently, IFN-alpha and IFN-gamma were shown to synergistically inhibit the proliferation of Renca in vitro and to synergize with IL-2 for treatment of localized Renca in vivo in euthymic but not athymic mice. Since CD8+ T cells are critical for the antitumor effects of FAA + rIL-2, current studies are focused on whether recognition of Renca-associated tumor antigen(s) occurs by T cells utilizing a select subset of T-cell receptor v-region genes. Alkalinization of Renca-bearing mice, in a manner analogous to that used for clinical trials of FAA, inhibited the ability of FAA to induce cytokine genes and proteins, as well as its therapeutic synergy with rIL-2. FAA induces cytokine genes directly in vitro concentrations of FAA greater than or equal to 100 (mu)g/ml preferentially induce the gene for IFN-gamma in CD8+ T cells, while the gene for IFN-alpha is preferentially induced in B cells. The TNF-alpha gene is induced in all subsets studied. Induction of gene expression was followed by the detection of IFN activity in the supernatants of treated splenic leukocytes. Since the production of cytokines contributes to the augmentation of cytotoxic effector cell activity, we have also studied the ability of FAA to augment NK and LAK activities in vitro. Pretreatment of mouse splenic leukocytes with 500 (mu)g/ml FAA alone induces some NK activity (12 LU30), while suboptimal (10 U/ml) and optimal (1000 U/ml) IL-2 yield 45 and 260 LU30 of NK activity, respectively. Pretreatment with 100 (mu)g/ml or 500 (mu)g/ml FAA enhances the ability of IL-2 to augment NK activity by 2-3 fold and enhances IL-2-induced LAK generation by approximately 2 fold. These results demonstrate that FAA can act directly as an immunomodulator, and suggest that in vitro models may be useful to elucidate its mechanism of action at the molecular level. Finally an apparently novel tumor cytostatic factor has been identified in lysates of rat RNK tumor lines and is being biochemically characterized prior to molecular cloning.